Hermetic sealing of glass substrates to create a vacuum or inert gas environment therebetween is typically made possible using barriers of usually glassy or metallic (e.g., eutectic) materials that are impermeable to ingress of gasses over a long time period, typically many orders of magnitude longer than the device operating lifetime. As will be understood, permeability typically involves two steps. These steps include dissolution and diffusion. Hermetic sealing helps keep, for example, water, other liquids, oxygen and other gaseous contaminant molecules out of packages that hold, for example, and without limitation, a vacuum (e.g., VIG window units, thermos flask, MEMS, and the like), or sensitive materials, such as, for example, and without limitation, organic emitting layers (e.g., used in OLED devices), semiconductor chips, sensors, optical components, or the like, held in an inert atmosphere. Gas tight packaging of the complex interiors of such assemblies has posed obstacles in the later stages of processing of such packages such as, for example, prior to pumping and tip fusing in the case of VIG window units, last processing steps in the manufacture of OLED devices, etc.
Some example VIG configurations are disclosed, for example, in U.S. Pat. Nos. 5,657,607, 5,664,395, 5,657,607, 5,902,652, 6,506,472 and 6,383,580, the disclosures of which are all hereby incorporated by reference herein in their entireties.
FIGS. 1 and 2 illustrate a typical VIG window unit 1 and elements that form the VIG window unit 1. For example, VIG unit 1 may include two spaced apart substantially parallel glass substrates 2, 3, which enclose an evacuated low-pressure space/cavity 6 therebetween. Glass sheets or substrates 2,3 are interconnected by a peripheral edge seal 4 that may be made of fused solder glass or the like, for example. An array of support pillars/spacers 5 may be included between the glass substrates 2, 3 to maintain the spacing of substrates 2, 3 of the VIG unit 1 in view of the low-pressure space/gap 6 present between the substrates 2, 3.
A pump-out tube 8 may be hermetically sealed by, for example, solder glass 9 or the like to an aperture/hole 10 that passes from an interior surface of one of the glass substrates 2 to the bottom of an optional recess 11 in the exterior surface of the glass substrate 2, or optionally to the exterior surface of the glass substrate 2. A vacuum is attached to pump-out tube 8 to evacuate the interior cavity 6 to a low pressure that is less than atmospheric pressure, for example, using a sequential pump down operation. After evacuation of the cavity 6, a portion (e.g., the tip) of the tube 8 is melted to seal the vacuum in low pressure cavity/space 6. The optional recess 11 may retain the sealed pump-out tube 8. Optionally, a chemical getter 12 may be included within a recess 13 that is disposed in an interior face of one of the glass substrates, e.g., glass substrate 2. The chemical getter 12 may be used to absorb or bind with certain residual impurities that may remain after the cavity 6 is evacuated and sealed. The getter 12 also acts in a manner so as to “mop up” gaseous impurities that may evolve during the environmental weathering of the unit.
VIG units with peripheral hermetic edge seals 4 (e.g., solder glass) are typically manufactured by depositing glass frit or other suitable material in a solution (e.g., frit paste) around the periphery of substrate 2 (or on substrate 3). This glass frit paste ultimately forms the edge seal 4. The other substrate (e.g., 3) is brought down on substrate 2 so as to sandwich spacers/pillars 5 and the glass frit solution between the two substrates 2, 3. The entire assembly including the glass substrates 2, 3, the spacers/pillars 5 and the seal material (e.g., glass frit in solution or paste), is then typically heated to a temperature of at least about 500° C., at which point the glass frit melts, wets the surfaces of the glass substrates 2, 3, and ultimately forms a hermetic peripheral/edge seal 4.
After formation of the edge seal 4 between the substrates, a vacuum is drawn via the pump-out tube 8 to form low pressure space/cavity 6 between the substrates 2, 3. The pressure in space/cavity 6 may be produced by way of an evacuation process to a level below atmospheric pressure, e.g., below about 10−4 Torr. To maintain the low pressure in the space/cavity 6, substrates 2, 3 are hermetically sealed via the edge seal and sealing off of the pump-out tube. Small high strength spacers/pillars 5 are provided between the transparent glass substrates to maintain separation of the approximately parallel glass substrates against atmospheric pressure. As noted above, once the space 6 between substrates 2, 3 is evacuated, the pump-out tube 8 may be sealed, for example, by melting its tip using a laser or the like.
High-temperature bonding techniques such as, for example, anodic bonding and glass frit bonding, as discussed above, have been widely used method for hermetically sealing (e.g., forming an edge seal) components made of silicon, ceramics, glass, or the like. The heat required for these high-temperature processes is typically in the range of about 300-600 degrees C. These conventional bonding techniques typically require oven-intensive bulk heating in which the entire device (including the glass and any components housed within the glass housing) comes to near thermal equilibrium with the oven for a seal to form. As a result, a relatively long period of time is required to achieve an acceptable seal. For example, as the device size L increases, the sealing time may typically increase on the order of L3. It is also the case that the most temperature sensitive component determines the maximum allowable temperature of the entire system. Thus, high-temperature sealing processes discussed above (e.g., anodic bonding and glass frit bonding) are not suitable for fabricating heat-sensitive components such as, for example, tempered VIG units and encapsulating sensitive components, such as, for example, OLED devices. In the case of tempered VIG units, the thermally tempered glass substrates of a VIG unit would rapidly lose temper strength in the high-temperature environment. In the case of an example OLED package, certain functional organic layers would be destroyed at temperatures of 300-600 degrees C. (sometimes even as low as 100° C.). In the past, one way to address this with high-temperature bulk sealing processes was to develop lower temperature frits, while still using bulk thermal equilibrium heating processes.
By way of background, glass frits and/or solders are typically mixtures of glass material and metallic oxides. Glass composition may be tailored to match the coefficient of thermal expansion (CTE) of the bonding substrates. Lead-based glasses are the most common bonding/sealing material/technique used commercially in cathode ray tubes (CRT), plasma displays and VIG window units. Lead-based glass frits are also among the least permeable glass sealing materials. Traditionally, these solders are based on glassy materials and de-vitrification is suppressed.
Glass frits or solders are typically made up of a base glass, a refractory filler and a vehicle. The base glass forms the bulk of the frit or solder. The filler reduces the CTE as well as matching it to the glass substrates to be joined. This matching enhances the mechanical strength, reduces interfacial stress and improves the crack resistance of the seal. The vehicle is typically made of a solvent (with surfactants) that provides fluidity for screen printing (e.g., for dispensing into gaps to be sealed and/or onto a surface to be sealed) and an organic binder.
Among one advantages of these types of glass frits or solders is that they include a relatively low melting point (e.g., in a range of about 480-520 degrees C.) glass that will stick to most semiconductor materials including, but not limited to, glass, silicon, silicon oxide, most metals and ceramics, making bonding techniques using these types of materials versatile and widely accepted.
There are many different types of commercially available glass frit materials having various melting points, CTEs, binders, and screen printing properties. However, almost all lower melting point formulations of glass frit or solder contain some lead. This may potentially become a drawback, as the U.S., EU, and Japan, for example, are severely limiting, if not forbidding, the use of lead in electronics manufacturing in the coming years. In the last few years, frits or solders based on bismuth oxides have had some success in replacing lead based frits, however the melting temperature (Tg) of these types of frits is still typically above about 450 degrees C. As with lead based frits, these bismuth oxide based frits cannot be used for fabrication of temperature sensitive devices using conventional oven bulk heating processes. Lower Tg (e.g., 375-390 degrees C.) frits based on vanadium barium zinc oxides (VBZ) have also been developed, including, but not limited to, VBaZn, V phosphates, SnZnPO4. However, widespread usage of these types of frits has been limited. Moreover, although such glass frits are an improvement over conventional approaches, they sometimes still have difficulties meeting stringent thermo-mechanical requirement of a low temperature all-glass peripheral seal. This is caused in part because low temperature glass solders usually are made of large ionic radii species do not readily diffuse into the glass surface at low processing temperatures and times.
Of course, it also will be appreciated that it would be desirable to provide VIG units capable of surviving harsh environments, e.g., those typically characterized by high operational temperatures, as well as exposure to shocks and vibrations, humidity, contaminants, radiation, and/or the like. For instance, the glazing industry subject materials to harsh environments with each extreme use posing its own challenges. For example, in skylights, glazing systems are subjected to extreme temperatures (150 degrees C.) and shocks and vibration loading related to wind loads. Indeed, ambient temperature near the VIG seal can reach in excess of 150 degrees C. with shock and vibration loading, and the ambient temperature in a building facade can be as high as 200 degrees C. Thus, it is challenging to provide an edge seal that provides long-term hermeticity, mechanical strength, and low possible thermal pathways.
Thus, it will be appreciated there is a need in the art for a seal processing technique that does not involve heating the entire article to be sealed to high temperature(s), and/or articles made in such example manners.
In certain example embodiments of this invention, a method of making a VIG unit is provided. A first layer stack is formed around peripheral edges of a first major surface of a first substrate, and a second layer stack is formed around peripheral edges of a first major surface of a second substrate. The first and second layer stacks are formed via activated energetic spray deposition and each include, in order moving away from the first major surfaces of the substrates on which they are formed, a layer comprising nickel and a layer comprising silver. Spacers are placed on the first major surface of the first substrate. A solid solder alloy pre-form is placed over and contacting the first layer stack. The first and second substrates are brought together such that the first major surfaces thereof face one another and form a subassembly. An edge seal is formed by reactively reflowing the solid solder alloy pre-form to cause material from the first and second layer stacks to diffuse into the solder alloy material, and vice versa. Following the formation of the edge seal, which then includes inter-metallic compounds, a cavity formed between the first and second substrates is evacuated in making the VIG unit.
In certain example embodiments of this invention, a method of making a VIG unit is provided. Multilayer coatings are formed around peripheral edges of first major surfaces of first and second substrates, with each said coating including, in order moving away from the respective substrate on which it is formed, a layer comprising nickel and a layer comprising silver, and with each said coating being selectively deposited using a high velocity wire combustion (HVWC) or high velocity oxy-fuel (HVOF) apparatus in an atmosphere including oxygen. Spacers are placed on the first major surface of the first substrate. A solder pre-form is placed over and contacting the coating formed on the first major surface of the first substrate. The first and second substrates are brought together such that the first major surfaces thereof face one another and form a subassembly. The subassembly is heated to a peak temperature of no more than 250 degrees C. and in an atmosphere less than atmospheric, in order to reflow the solder pre-form and form an edge seal. Following the formation of the edge seal, a cavity formed between the first and second substrates is evacuated in making the VIG unit.
In certain example embodiments of this invention, a VIG unit is provided. The VIG unit comprises first and second substantially parallel spaced apart substrates, with at least one of the first and second substrates being a heat treated glass substrate. Spacers are provided between the first and second substrates. An edge seal comprises an alloy material including Sn and at least one other material selected from the group consisting of post-transition metals or metalloids; Zintl anions from group 13, 14, 15, or 16; and transition metals and, on each side thereof and in order moving away from the alloy material and towards the first and second substrates, respectively, at least one inter-metallic (IMC) layer, an activated energetic spray deposition deposited silver-inclusive layer, and an activated energetic spray deposition deposited nickel-inclusive layer. The silver-inclusive layers and the nickel-inclusive layers (a) individually have an adhesion or bond strength of at least 10 MPa, an RMS roughness (Ra) of less than 2 microns, and a porosity of less than 2%, and (b) collectively have an adhesion or bond strength of at least 20 MPa, an RMS roughness (Ra) of less than 2 microns, and a porosity of less than 2% (e.g., when deposited).
The features, aspects, advantages, and example embodiments described herein may be combined to realize yet further embodiments.